There is known an acoustic wave element having a piezoelectric substrate and an IDT (InterDigital Transducer) provided on a major surface of the piezoelectric substrate. Such an acoustic wave element is utilized in for example a transmitting filter, receiving filter, or the like of a branching filter.
In an acoustic wave element, the electrical characteristics sometimes fall due to an electrical distorted wave generated due to nonlinearity of the element. For example, in a branching filter using an acoustic wave element, an interfering wave which is out of the transmission band and reception band and a transmission wave are mixed to cause a distorted wave contained in the reception band. This distorted wave is called inter-modulation distortion (IMD) and is one of the causes of a drop in the quality of communication (SN ratio) of a wireless communication apparatus. Other than this, harmonic distortion having a frequency which is a whole multiple of the transmission wave is generated. There is also a possibility of obstruction of communication of another wireless communication apparatus or another problem by this.
Therefore, for suppressing the drop of the SN ratio due to the distorted wave, there is known a method of dividing a serial resonator or parallel resonator of a ladder type filter which configures the branching filter without a change of electrostatic capacity (for example Patent Literature 1). This is to divide the serial resonator or parallel resonator and thereby disperse the voltage applied to the resonator to suppress the distorted wave.
Note that, although not a citation relating to the art of suppressing the distorted wave, Patent Literature 2 discloses a capacitance element which is provided on a major surface of a piezoelectric substrate and is connected parallel to an IDT.
However, when dividing a resonator without a change of electrostatic capacity, compared with that before division, the resonator becomes larger in size and consequently the acoustic wave element becomes larger in size.